1. Field of the Invention
The present invention generally relates to engine block heaters that are used to keep the engine of an automobile warm when the automobile is not running. More particularly, the present invention relates to engine block heaters with safety features that are intended to prevent the automobile from being used while the engine block heater is in operation.
2. Description of the Prior Art
In many areas of the world, temperatures fall well below freezing for many months out of the year. In many such locations, there are days when temperatures dip below zero degrees Fahrenheit. During such extreme cold weather, it is difficult to start an engine of a typical stock-model automobile. In such extreme cold weather, the power of the automobile's battery is diminished. Furthermore, the oil in the engine becomes highly viscous and thus the crankshaft becomes hard to turn. The temperature weakened battery often lacks the power needed to turn an engine through the thick oil and the engine fails to start. The cold weather also greatly affects the ability of diesel engines to cause combustion. In extreme cold weather, many commercial diesel engines lack the starting power needed to create enough engine compression to ignite the diesel fuel and start the engine.
In areas where extreme cold temperatures are common, many people keep their automobiles in heated garages. However, not everyone has access to a heated garage. Many times such people use block heaters in their automobiles. Block heaters are electrical heating elements that heat the oil and liquid coolant contained within the automobile's engine. By heating the oil and the engine coolant, the oil is kept thin and the coolant unfrozen. The engine can therefore be started easily regardless of the outside temperature.
Traditional block heaters are electrically powered and require that an electrical extension cord lead to the engine of the automobile. A problem occurs when people forget to disconnect the electrical cord that powers the block heater and drive the automobile while the electrical cord is still connected. When this happens, the electrical cord pulls taut and violently disconnects. This often causes damage to the automobile, the electrical receptacle and/or the cord connecting the automobile to the electrical receptacle.
Over the years, various systems have been developed to inform a driver that the vehicle they have entered contains an electrical block heater and is currently plugged into a receptacle with an extension cord. For instance, in U.S. Pat. No. 3,744,046 to Tamasi, entitled Engine Heater Monitor And Control System, a system is shown that uses different colored lights to inform a driver about the status of a block heater. Similar systems are shown in U.S. Pat. No. 5,115,116 to Reed, entitled Vehicle Preheating System and U.S. Pat. No. 6,225,893 to Caissia, entitled Alarm System For Engine Block Heater. In both the Reed patent and the Caissia patent, systems are shown that provide alarm signals if the automobile is started while the engine block heater is still engaged.
A problem associated with the prior art systems is that a person who is in a hurry may start an automobile and drive the vehicle a few feet before they notice an alarm light or alarm signal. This is particularly true if the automobile is parked in a garage and a person is turned to look backwards as they back the automobile out of the garage. By the time a person turns to see a warning light on a dashboard, a person may have already caused serious damage to the automobile, the wall power receptacle and/or the cord that leads to the engine block heater.
A need therefore exists for an improved engine block heater system that prevents the automobile from being started when the engine block heater is in operation. In this manner, the automobile cannot be inadvertently driven away while the engine block heater is still connected to an outlet. Furthermore, by preventing the automobile from starting while the engine block heater is in use, the driver of the automobile is provided with the ultimate reminder to disconnect the engine block heater from the automobile.